Inconsistent with prevailing models for nonsense-mediated mRNA decay (NMD) in mammals, the mRNA levels of immunoglobulin-mu (Ig-mu) genes with premature termination codons (PTCs) in the penultimate exon are still reduced by NMD when the intron furthest downstream is deleted. As in yeast, this exon junction complex-independent NMD of Ig-mu mRNAs depends on the distance between the termination codon and the poly(A) tail and suggests an evolutionarily conserved mode of PTC recognition.

DNA double-strand breaks (DSBs) initiate meiotic recombination in Schizosaccharomyces pombe and in other organisms. The Rec12 protein catalyzes the formation of these DSBs in concert with a multitude of accessory proteins the role of which in this process remains to be discovered. In an all-to-all yeast two-hybrid matrix analysis, we discovered new interactions among putative members of the meiotic recombination initiation complex. We found that Rec7, an axial-element associated protein with homologies to Saccharomyces cerevisiae Rec114, is interacting with Rec24. Rec7 and Rec24 also co-immunoprecipitate in S. pombe during meiosis. An amino acid change in a conserved, C-terminal phenylalanine in Rec7, F325A interrupts the interaction with Rec24. Moreover, rec7F325A shows a recombination deficiency comparable to rec7Delta. Another interaction was detected between Rec12 and Rec14, the orthologs of which in S. cerevisiae Spo11 and Ski8 interact accordingly. Amino acid changes Rec12Q308A and Rec12R309A disrupt the interaction with Rec14, like the according amino acid changes Spo11Q376A and Spo11RE377AA loose the interaction with Ski8. Both amino acid changes in Rec12 reveal a recombination deficient rec12 (-) phenotype. We propose that both Rec7-Rec24 and Rec12-Rec14 form subcomplexes of the meiotic recombination initiation complex.

The majority of functionally characterized plant disease resistance genes are of the nucleotide-binding site (NBS)-LRR gene family, encoding proteins with a central NBS domain, a carboxy-terminal leucine-rich repeat domain, and a variable N-terminal region with or without homology to the Toll interleukin 1-like receptor (TIR) domain, referred to as TIR and non-TIR resistance gene homologues (RGH), respectively. Degenerate primers designed from conserved motifs within the NBS sequence were used to amplify, clone and sequence NBS-RGH from the sweetpotato genome. Two hundred and twenty-five distinct sweetpotato NBS sequences with similarity to known RGH genes were identified. Additional 50 sweetpotato RGHs were mined from the public genomic sequence database. Thus, a total of 275 RGH sequences were obtained using both PCR-based method and data-mining approach, from which 237 were non-TIR sequences organized into 35 singletons and 35 groups after reduced to 90% nucleotide identity, and 38 were TIR sequences divided into three primary phylogenetic clades. A bias of non-TIR vs. TIR was observed not only in genomic RGH sequences, but also in expressed sequence tags-RGH sequences. A subset of sweetpotato non-TIR RGH genes contained a conserved intron within the NBS sequences. The exploration of RGH diversity enables resistance gene evolutionary study and may facilitate the isolation of new and functional alleles. These new RGH sequences provided a resource of candidate genes and molecular markers for disease resistance research in sweetpotato.